This application is based on and claims priority to Japanese Patent Application No. 2000-074225, filed Mar. 16, 2000, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to a cooling system for an outboard motor. More particularly, the present invention relates to a cooling system for an engine and a plurality of engine components of an outboard motor.
2. Description of Related Art
Typically, an outboard motor comprises an engine disposed atop a drive unit of the motor. To propel the associated watercraft, the engine drives a propulsion device placed in a submerged position through a proper drive mechanism. The engine usually has an engine body and a plurality of components. The engine body normally comprises a cylinder block, a cylinder head assembly and a crankcase assembly. At least one combustion chamber, and often more than one combustion chamber, is provided within the engine. Occasionally, part of an exhaust passage is unitarily formed with the engine body. Other engine components can include, for example, air intake conduits, fuel supply conduits, lubricant delivery conduits and a power generator, which all relate to the operation of the engine.
The engine body comprising the exhaust part and the foregoing engine components usually build much heat during the engine operations. The heat can accumulate therein unless properly removed and excessive heat can jeopardize normal engine operations. Typical engines thus have a cooling system that can cool the heated portions of the engine body and engine components. Various cooling systems are practicable.
One type of cooling system introduces water from outside of the motor and cools the engine body first because the engine body is subjected to greater temperature levels when compared to peripheral engine components. The water that has cooled the engine body then flows to the respective peripheral engine components. Another type of cooling system has a direct conduit branching off upstream of the engine body to supply fresh water to a peripheral engine component.
For instance, U.S. Pat. Nos. 5,975,032 and 5,980,340 disclose the former type of cooling system, while U.S. Pat. No. 5,438,962 discloses the latter type of cooling system. Japanese Laid-Open Patent Publication No. Hei 6-42345, published on Feb. 15, 1994, also discloses a rectifier-regulator cooling structure using fuel or water flowing through a cooling passage. Furthermore, Japanese Laid-Open Patent Publication No. Hei 11-324696, published on Nov. 26, 1999, discloses a cooling system that can cool a power generator and a high pressure fuel pump. An auxiliary water supply passage branches off from a main water supply passage to the generator and then to the fuel pump. The water that has cooled these two components then is discharged through a submerged discharge port.
In engine design for outboard motors, there is an increasing emphasis on obtaining high performance in output and more effective emission control. This trend has resulted in employing, for example, a multi-cylinder, fuel injected, four-cycle engine. This type of engine must have a greater number of engine components or larger sizes thereof than those of conventional engines. The engine body and the engine components of this new type of engine also produce greater heat levels than two-stroke engines. Particularly, if the components are one-sided or if the components are disposed such that only one side is cooled, the engine can develop disadvantageous hot zones. The hot zones can result in distortion of the engine body or engine components, or disruption of proper engine operations. The forgoing conventional cooling systems are not enough to resolve this problem.
A need therefore exists for an improved cooling system for an outboard motor that can cool an engine body and engine components efficiently and that can maintain a relatively good heat balance in connection with the respective sides.
In addition, if a cooling system malfunctions such that water can no longer be supplied to the portions that need the water for cooling, the engine can overheat. Engine overheat can result in, for example, seizure of pistons and malfunction of engine components. A pilot water discharge is useful to let the operator know of cooling system abnormalities, such as plugging. U.S. Pat. No. 5,823,835 discloses such a pilot water discharge. In this arrangement, a pilot discharge port is positioned above the water line and a small amount of cooling water that has passed through cooling jackets disposed in the engine body is expelled through this pilot discharge port as visual confirmation to the operator that cooling water is being properly supplied to the engine body.
As noted above, the engine body produces heat greater than the engine components, and in addition, the heat of the recent multiple cylinder engine is higher than before. The elevated temperature of the pilot water can discolor the coating that covers a surface of the housing or cowling of the outboard motor. For instance, in the region of the port, the high temperature water can discolor the outward appearance of the motor or cause scaling and the like.
Another need thus exists for an improved cooling system that has a pilot water discharge that does not adversely affect to a large degree the outward appearance of the outboard motor.
Further, the foregoing engine components are generally formed with metal material, such as, for example, aluminum based alloy cast material as well as the engine body. Otherwise, at least part of the engine components is formed with metal material for the heat exchange purpose although the rest part of the components is made of other material such as plastic. When the motor is used on the sea, seawater, i.e., salt water, is supplied to the engine components. The salt water, however, is likely to corrode bodies of the engine components that are made of metal material and hence can damage their primary functions.
A further need therefore exists for an improved cooling system for an outboard motor that can inhibit corrosion from encroaching engine components.
Accordingly, one aspect of the present invention involves an internal combustion engine for an outboard motor comprising an engine body, at least three engine components disposed around the engine body, and a water cooling system for cooling both the engine body and the engine components. The cooling system comprises a first water passage arranged to cool the engine body and a second water passage branching off from the first water passage upstream of the engine body and extending through the at least three engine components. A first of the at least three engine components is generally positioned above the engine body while a second and a third of the at least three engine components is generally positioned on a different side of the engine body relative to one another.
Another aspect of the present invention involves an internal combustion engine comprising an engine body, a plurality of engine components disposed around the engine body, and a water cooling system for cooling both the engine body and the engine components. The cooling system comprises a first water passage arranged to cool the engine body and a second water passage branching off from the first water passage upstream of the engine body and extending through the plurality of engine components in series. The first and second water passages have separate discharge ports that are located remotely from each another and the water discharge port of the second water passage is positioned next to the engine body.
A further aspect of the present invention involves an internal combustion engine comprising an engine body, a plurality of engine components being disposed around the engine body, and a water cooling system arranged to cool both the engine body and the plurality of engine components. The cooling system comprises a first water passage arranged to cool the engine body and a second water passage branching off from the first water passage upstream of the engine body and extending through the plurality of engine components. The plurality of engine components are made of a metal material with the second water passage in part being defined by tubular members made of a corrosion-resistant material. The respective tubular members are at least partially embedded in respective bodies of the engine components.
Another aspect of the present invention involves an internal combustion engine comprising an engine body, a plurality of engine components disposed around the engine body, and a cooling system for cooling both the engine body and the plurality of engine components. The cooling system comprises a first coolant passage arranged to cool the engine body and a second coolant passage branching off from the first coolant passage upstream of the engine body and extending through at least three of the plurality of engine components. The at least three engine components comprising a first engine component positioned at least above the engine body and a two engine components each positioned on two sides of the engine body so as to be spaced apart from each other.
An additional aspect of the present invention involves an outboard motor comprising an engine body, a plurality of engine components disposed around the engine body, and a water cooling system comprising a water inlet disposed lower than the engine body so as to introduce the water into the cooling system. A first water passage is arranged to cool the engine body and a second water passage is arranged to cool the plurality of engine components. The first water passage has a first water discharge port positioned closer to the water inlet than to the engine body and the second water passage has a second water discharge port positioned closer to the engine body than to the water inlet.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follows.